Conveyor chains for heavy duty conveyors conventionally include single and dual links pivotally connected in an alternating relationship along an axis of the chain. The single link is conventionally referred to as a "dog bone" link in that it has a smaller intermediate portion and opposite ends that are enlarged. At each enlarged end, adjacent ends of the adjacent pair of dual links are pivotally connected to the enlarged end of the dog bone single link by an associated connection pin that extends vertically. Three basic types of conveyors incorporate this type of conveyor chain. One of these types of conveyors is referred to as an overhead monorail and is suspended by trollies from a horizontally extending beam having flanges on which rollers of the trollies ride. Another of these types of conveyors is referred to as an overhead power and free and is basically the same as the overhead monorail except that another horizontal beam below the conveyor chain supports load trollies which are connected to and detached from the conveyor chain by clutch dogs at stations along which the conveyor chain conveys loads supported by the load trollies. A third type of these conveyors is referred to as an inverted power and free and is basically the same as the overhead power and free except for the fact that the conveyor chain is supported for movement above a horizontal beam on which trolley rollers are supported and load trollies are supported above the chain by another horizontal beam for movement upon connection thereof to the chain by clutch dogs as well as being released from the chain by the clutch dogs when necessary.
When conveyor chains of the type involved with the present invention are negotiating certain areas of the conveyor, wear of the conveyor components involved can excessively tension the chain and thereby eventually cause failure. For example, a conveyor chain negotiating a turn is moved over a roller which if not properly greased can produce friction and/or wear that may tension the chain beyond its normal operating tension. Any failure of the chain shuts down the conveyor and thereby causes an enormous financial loss. This is especially the case if the conveyor involved feeds components to other conveyor lines of the factory and thereby also shuts down the other conveyor lines.
In order to sense conveyor chain loading in order to permit proper maintenance of the conveyor, it has previously been proposed to utilize strain gauges with links of the conveyor chain. See, for example, U.S. Pat. No. 4,566,339 Davidson et al and U.S. Pat. No. 4,803,886 May et al, and United Kingdom Patent application 2,041,549 of inventor Cecil J. Austen. Each of these prior references discloses a conveyor chain wherein the single link has strain gauges applied thereto so as to sense the loading, and the load signal sensed may be sent by telemetry or otherwise for monitoring. Since the strain gauges utilized with these prior art references are applied directly to the link that carries the load, the load reading is not particularly sensitive.
Other prior art references which were noted during the investigation conducted for the present invention, but which are not believed to be analogous prior art because the transducers involved are not for use with a conveyor chain, are set forth below along with a description of the use for which the transducer is designed.
U.S. Pat. No. 2,590,626 Jones discloses a tension yoke for compression load weighing stations wherein a compression column on which strain gauges are mounted is compressed by a load transmitting member located in engagement with an inner flat link located between two outer flat links.
U.S. Pat. No. 3,100,290 Propper discloses a columnar stress sensing member which includes a strain gauge element located between a stress applying part and a stress resisting part with strain gauges mounted within a cylindrical surface of the strain element.
U.S. Pat. No. 3,246,510 Ruge discloses a non-linearity compensation means for electrical strain gauge transducer wherein one disclosed embodiment has a transducer element located between two connectors where a force is applied and having a central round opening in which strain gauges are mounted to sense the loading.
U.S. Pat. No. 3,559,474 Gurol et al discloses a force transducer load cell which includes an annular member having an outer surface on which strain sensitive elements are mounted to sense loading.
U.S. Pat. No. 4,079,624 Kurtz discloses a load washer transducer assembly which also has an annular shape and an outer surface on which sensor elements are mounted.
U.S. Pat. No. 4,282,762 Zenker discloses a load sensing transducer which includes an annular member on which strain gauges are mounted to sense loading.
U.S. Pat. No. 4,770,049 Jones et al discloses load measuring devices which have annular shapes having strain gauges mounted on outwardly facing surfaces.
U.S. Pat. No. 4,420,755 Primbs, Jr. discloses a telemetry load link assembly for measuring strain in a load cable between an aircraft and a recovered object.